The present invention relates to transportable enclosures for reducing particle contamination during manufacture, storage or transportation of components and more particularly to standardized mechanical interface (SMIF) systems employing a vapor drain system for removing chemical vapors and components from within the enclosure.
Chemical vapor contaminants are known to alter the processes used to manufacture sensitive devices such as microcircuitry. Such chemical vapor contaminants have historically been inadequately addressed. These vapor contaminants originate from a variety of sources, including the enclosures used to protect components from particulate contamination. Outgassing of plastics, adhesives and sealant materials can make the enclosure itself a source of chemical contaminants. In addition, externally produced vapors are capable of contaminating an open enclosure. Later, when the enclosure contains a sensitive component, such as a semiconductor wafer, these vapors can be re-emitted and contaminate the wafer.
The import of particulate contamination on the manufacture of components having very tight tolerances, such as disk files and microcircuitry, is well known. Processes are carefully controlled to reduce by many orders of magnitude the quantity of particles in the manufacturing environment as evidenced by the increased use of "clean rooms" and by improvements in particle detection and removal technology.
Chemical contamination is beginning to be recognized as a major factor in manufacturing operations. Such contamination was first recognized in process chemicals, such as impurities in gases used in semiconductor device manufacture and in solvent residues.
Process contamination caused by environmental air-borne vapors is also a growing problem. Such vapors are everywhere in the environment at low concentrations. The origin of the vapor is diverse and includes plasticizer vapors, process materials from elsewhere in a factory, chemicals used in cleaning and air conditioning systems, cosmetics, adhesives and chemicals used in neighboring factories and in agriculture. These contaminants can degrade manufacturing by affecting the sensitivity of lithographic, etch and other processes, interfering with adhesion between surfaces, altering the wetability of surfaces, reducing effectiveness of cleaning processes, interfering with chemical reactions and inducing corrosion of metallurgy.
Some chemical compounds are capable of travelling as vapors which deposit a mono-molecular layer on the wafer, which degrades subsequent wafer manufacturing processes and product quality. An important class of organic compounds has a molecular mass between approximately 150 and 600 AMU (atomic mass units) and non-specific chemical reactivity. These compounds emit significant vapors add adhere as a mono-molecular layer to cause product degradation. One such compound is di-alkyl-phthalates, which is a widely used plasticizer. In contrast, organic compounds having much larger molecular masses typically do not emit significant vapor and organic compounds having much smaller molecular mass typically do not adhere sufficiently to a surface, and hence both types of components usually do not pose a problem.
Another class of relatively light compounds has specific chemical reactivity. For example, many metals are attacked by halogenated solvents (e.g., di-chloro-methane or tri-chloro-ethane) and by organic acids (e.g., acrylic or benzoic acids).
Vapor self-contamination is particularly relevant. Even a sealed enclosure traps and accumulates vapors. The vapors are emitted by enclosure materials (such as plastics, adhesives, sealants and their trace components), external vapors absorbed onto the enclosure surfaces and into seals when the enclosure is open, and vapors emitted by nascent products.
Process chemicals and enclosure materials should be chemically selected to minimize these problems. In view of practical restraints, it is very difficult to eliminate contamination from trace vapors and mono-molecular layers solely by material selection. Moreover, vapor emission is only one of the criteria which must be met by nascent process materials such as resists.
In the complex processes involved in the fabrication of microcircuitry, there is a recent trend toward containing the components in sealed enclosures which are generally kept closed, and are opened only briefly and intermittently during fabrication. This manufacturing method has been developed for maintaining a particulate free environment. Unfortunately, these enclosures have the unintended result of concentrating vapor contamination. This effect has been inadequately understood in the prior art.
Such sealed enclosures are sometimes referred to as standardized mechanical interface (SMIF) systems. SMIF systems are described in U.S. Pat. No. 4,739,882 assigned to Asyst Technologies Inc. and in U.S. Pat. No. 4,532,970 and U.S. Pat. No. 4,534,389 both assigned to Hewlett-Packard Company, which patents are each incorporated herein by reference.
The present invention overcomes the difficulties encountered by heretofore known enclosures by equipping each enclosure or SMIF system with a device which acts to remove vapors and shall be referred to hereinafter as a vapor removal element. While the invention is primarily intended for use in connection with a SMIF system, the invention is equally applicable for use with any sealed enclosure used for manufacturing, storing or transporting of components sensitive to chemical vapors.
In addition to semiconductor, mechanical, electrical and electronic products and processes, the present invention has application to any product with potential or known sensitivity to vapor borne contamination, such as pharmaceuticals, clinical diagnostic and therapeutic products, chemicals and genetically engineered products.